1. Field of the Invention
The invention relates to input/output devices in an integrated circuit (IC) product and more particularly to input/output devices capable of blocking external interference signals from other input/output devices.
2. Description of the Related Art
As mobile communication has become increasingly popular, radio frequency (RF) technology has progressed and various wireless protocols, such as Bluetooth, 802.11a/b/g, GSM, TDMA, have been introduced. Some wireless protocols transmit and receive signals simultaneously, while others, such as TDMA, require that signals be transmitted and received in turns or utilizing different time slots.
For protocols requiring separate of transmission and reception, a transmitter in an RF IC is turned on while a receiver in the same RF IC is turned off, and vice versa. Ideally the transmitter and receiver operate independently and do not interfere with each other. The board on which the RF IC is mounted, however, provides a signal path that causes an unwanted feedback signal from a receiver to a transmitter, thus, output signal quality suffers during signal transmission.
FIG. 1 illustrates the origin of the feedback signal during signal transmission. In a transmission mode, transmitter 12 on an RF IC amplifies an internal signal to generate output signal 20 for radiation by antenna 16 on a board. The board typically comprises metal straps, vias and the like for constructing signal paths to convey signals. Although the signal path for output signal 20 may not be directly shorted by a signal path for a receiver in a receiving mode, the conductors on the board inevitably form parasitic capacitors that provide leakage paths for signals, particularly for high power signals. For example, parasitic capacitor 18 in FIG. 1 provides a leakage path for output signal 20, such that leakage signal 22, which is part of the output signal 20, jumps to conductor 19 on the board and heads to the input of receiver 14 in the same RF IC. Leakage signal 22 may be transferred by receiver 14 to feedback signal 10 and sent to transmitter 12 finally deteriorating output signal 20. That kind of leakage signal 22 or feedback signal 10 should be removed or minimized, if possible.